Medium identification device, image forming apparatus, method of identifying medium, and computer program product

ABSTRACT

A medium identification device identifies a type of a recording medium used for image formation. The medium identification device includes: a two-dimensional image sensor that captures an image of the recording medium; and an identifying unit that obtains a glossiness evaluation value indicating glossiness of the recording medium, a surface roughness evaluation value indicating surface roughness of the recording medium, and a coloring evaluation value indicating coloring of the recording medium, using image data of a specular reflection region reflecting specular reflection light from the recording medium and image data of a diffused reflection region reflecting diffused reflection light from the recording medium, the regions being in the image of the recording medium, and identifies the type of the recording medium by combining determination using the glossiness evaluation value, determination using the surface roughness evaluation value, and determination using the coloring evaluation value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of, and claims thebenefit of priority under 35 U.S.C. §120 from, U.S. application Ser. No.14/812,045, filed Jul. 29, 2015, which claims the benefit of priorityunder 35 U.S.C. §119 from Japanese Patent Application No. 2014-158015filed Aug. 1, 2014. The entire contents of each of the aboveapplications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a medium identification device, animage forming apparatus, a method of identifying a medium, and acomputer program product.

2. Description of the Related Art

Regarding an image forming apparatus that forms an image on a recordingmedium, known is a technique for automatically identifying a type of arecording medium to be used and changing a condition for an imageforming process according to the identified type of the recording mediumto perform optimum image formation on the recording medium to be used.

For example, Japanese Patent Application Laid-open No. 2002-182518 andJapanese Patent Application Laid-open No. 2003-302885 disclose an imageforming apparatus that identifies a type of a recording medium using amethod of detecting surface smoothness of the recording medium by usingan image of the recording medium captured with a CMOS sensor, andvariably controls a developing condition, a transferring condition, or afixing condition. Japanese Patent Application Laid-open No. 2007-55814discloses an example for identifying the type of the recording medium,in which surface smoothness and reflectivity of the recording medium isobtained by detecting reflected light from the recording medium with aCMOS sensor, and a thickness of the recording medium is obtained bydetecting transmitted light that transmits through the recording mediumwith the CMOS sensor.

However, types of recording media that can be used for image formationhave been increasing in recent years, and there are many types thatcannot be identified according to the related art. Thus, desired is anovel technique for identifying more variety of recording media.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least partially solve theproblems in the conventional technology.

A medium identification device identifies a type of a recording mediumused for image formation. The medium identification device includes: atwo-dimensional image sensor that captures an image of the recordingmedium; and an identifying unit that obtains a glossiness evaluationvalue indicating glossiness of the recording medium, a surface roughnessevaluation value indicating surface roughness of the recording medium,and a coloring evaluation value indicating coloring of the recordingmedium, using image data of a specular reflection region reflectingspecular reflection light from the recording medium and image data of adiffused reflection region reflecting diffused reflection light from therecording medium, the regions being in the image of the recordingmedium, and identifies the type of the recording medium by combiningdetermination using the glossiness evaluation value, determination usingthe surface roughness evaluation value, and determination using thecoloring evaluation value.

A method of identifying a medium is executed by a medium identificationdevice that comprises a two-dimensional image sensor. The methodincludes: capturing an image of a recording medium with thetwo-dimensional image sensor; and obtaining a glossiness evaluationvalue indicating glossiness of the recording medium, a surface roughnessevaluation value indicating surface roughness of the recording medium,and a coloring evaluation value indicating coloring of the recordingmedium, using image data of a specular reflection region reflectingspecular reflection light from the recording medium and image data of adiffused reflection region reflecting diffused reflection light from therecording medium, the regions being in the image of the recordingmedium, and identifying a type of the recording medium by combiningdetermination using the glossiness evaluation value, determination usingthe surface roughness evaluation value, and determination using thecoloring evaluation value.

A computer program product includes a non-transitory computer-readablemedium containing an information processing program. The program causesa computer of a medium identification device that comprises atwo-dimensional image sensor, to implement: a function of capturing animage of a recording medium with the two-dimensional image sensor; and afunction of obtaining a glossiness evaluation value indicatingglossiness of the recording medium, a surface roughness evaluation valueindicating surface roughness of the recording medium, and a coloringevaluation value indicating coloring of the recording medium, usingimage data of a specular reflection region reflecting specularreflection light from the recording medium and image data of a diffusedreflection region reflecting diffused reflection light from therecording medium, the regions being in the image of the recordingmedium, and identifying a type of the recording medium by combiningdetermination using the glossiness evaluation value, determination usingthe surface roughness evaluation value, and determination using thecoloring evaluation value.

The above and other objects, features, advantages and technical andindustrial significance of this invention will be better understood byreading the following detailed description of presently preferredembodiments of the invention, when considered in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating the inside of an image formingapparatus being seen through;

FIG. 2 is a top view illustrating a mechanical configuration of theinside of the image forming apparatus;

FIG. 3 is a diagram for explaining an arrangement example of recordingheads mounted on a carriage;

FIG. 4A is a vertical cross-sectional view of a colorimetric camera;

FIG. 4B is a plan view of a bottom face of a housing of the colorimetriccamera viewed from the X1 direction in FIG. 4A;

FIG. 5 is a block diagram illustrating a schematic configuration of acontrol mechanism of the image forming apparatus;

FIG. 6 is a block diagram illustrating a configuration example of acontrol mechanism of the colorimetric camera;

FIG. 7 is a flowchart illustrating an operation procedure of thecolorimetric camera in identifying a medium;

FIGS. 8A and 8B are diagrams illustrating an example of an image of arecording medium captured by a two-dimensional image sensor underillumination of a second light source;

FIG. 9 is a diagram illustrating an example of a luminance histogram ofa specular reflection region;

FIG. 10 is a diagram illustrating a relation between types of therecording media and a peak value of the luminance histogram of thespecular reflection region;

FIG. 11 is a diagram three-dimensionally illustrating a luminancedistribution in a diffused reflection region in a case in which therecording medium is a “mat film”;

FIG. 12 is a diagram illustrating an example of the luminance histogramof the diffused reflection region;

FIG. 13 is a diagram three-dimensionally illustrating the luminancedistribution in the diffused reflection region in a case in which therecording medium is “tracing paper”;

FIG. 14 is a diagram illustrating an example of the luminance histogramof the diffused reflection region;

FIG. 15 is a diagram illustrating a relation between the types of therecording media and a value of a standard deviation of the luminancehistogram of the diffused reflection region;

FIG. 16 is a diagram three-dimensionally illustrating the luminancedistribution in the specular reflection region in a case in which therecording medium is “semi-glossy paper”;

FIG. 17 is a diagram three-dimensionally illustrating a residualdistribution;

FIG. 18 is a diagram illustrating an example of a histogram of aresidual;

FIG. 19 is a diagram illustrating a relation between the types of therecording media and a value of a standard deviation of the histogram ofthe residuals of the specular reflection region;

FIGS. 20A to 20D are diagrams illustrating a coordinate range in an RGBcolor space that is set for each type of the registered recordingmedium;

FIGS. 21A to 21D is a diagram illustrating a coordinate range in anL*a*b* color space that is set for each type of the registered recordingmedium;

FIG. 22 is a flowchart illustrating an example of a processing procedureperformed by an identifying unit;

FIG. 23 is a diagram for explaining a relation between an example of theprocessing procedure performed by the identifying unit andidentification results;

FIG. 24 is a diagram for explaining a relation between another exampleof the processing procedure performed by the identifying unit andidentification results;

FIG. 25 is a diagram illustrating a relation between an optimum printingtype, and the types of the recording media and printing modes;

FIG. 26 is a diagram illustrating a discharging type and resolutioncorresponding to each printing type;

FIG. 27 is a diagram illustrating a relation between the types of therecording media and the printing mode that is automatically set;

FIG. 28 is a flowchart illustrating an example of processing ofgenerating and storing information for identifying a type of an unknownrecording medium;

FIG. 29 is a flowchart illustrating an operation of the image formingapparatus after the processing of identifying the type of the recordingmedium is ended;

FIG. 30A is a vertical cross-sectional view of a colorimetric cameraaccording to a first modification;

FIG. 30B is a vertical cross-sectional view of the colorimetric cameraaccording to the first modification;

FIG. 31 is a vertical cross-sectional view of a colorimetric cameraaccording to a second modification; and

FIG. 32 is a diagram illustrating a schematic configuration of an imageforming system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following describes an embodiment of a medium identification device,an image forming apparatus, a method of identifying a medium, and acomputer program product in detail with reference to the attacheddrawings. The following embodiment describes an example of causing acolorimetric camera to have a function as a medium identification deviceaccording to the present invention, the colorimetric camera beingmounted on an image forming apparatus constructed as an inkjet printerand having a function of capturing an image of a colorimetric patternformed on a recording medium by the image forming apparatus to calculatea colorimetric value.

Mechanical Configuration of Image Forming Apparatus

First, the following describes a mechanical configuration of an imageforming apparatus 100 according to the embodiment with reference toFIGS. 1 to 3. FIG. 1 is a perspective view illustrating the inside ofthe image forming apparatus 100 being seen through. FIG. 2 is a top viewillustrating a mechanical configuration of the inside of the imageforming apparatus 100. FIG. 3 is a diagram for explaining an arrangementexample of recording heads 6 mounted on a carriage 5.

As illustrated in FIG. 1, the image forming apparatus 100 according tothe embodiment includes the carriage 5 that reciprocates in a mainscanning direction (the arrow A direction in FIG. 1). The carriage 5 issupported by a main guide rod 3 extended along the main scanningdirection. A connecting piece 5 a is provided to the carriage 5. Theconnecting piece 5 a is engaged with a sub-guide member 4 arranged inparallel with the main guide rod 3 and stabilizes a posture of thecarriage 5.

As illustrated in FIG. 2, the carriage 5 includes a recording head 6 ythat discharges yellow ink, a recording head 6 m that discharges magentaink, a recording head 6 c that discharges cyan ink, and a recording head6 k that discharges black ink (hereinafter, when the recording heads 6y, 6 m, 6 c, and 6 k are collectively referred to, they are referred toas a “recording head 6”) mounted thereon. The recording head 6 ismounted on the carriage 5 so that a discharge face (nozzle face) thereoffaces downward (toward a recording medium M).

A cartridge 7 serving as an ink supplier for supplying ink to therecording head 6 is not mounted on the carriage 5, and arranged at apredetermined position in the image forming apparatus 100. The cartridge7 is coupled to the recording head 6 with a pipe (not illustrated), andink is supplied from the cartridge 7 to the recording head 6 through thepipe.

The carriage 5 is coupled to a timing belt 11 stretched between adriving pulley 9 and a driven pulley 10. The driving pulley 9 is rotatedby driving of the main scanning motor 8. The driven pulley 10 has amechanism that adjusts a distance between the driven pulley 10 and thedriving pulley 9, and serves to give predetermined tension to the timingbelt 11. The carriage 5 reciprocates in the main scanning direction whenthe timing belt 11 is fed by the driving of the main scanning motor 8.For example, as illustrated in FIG. 2, the movement of the carriage 5 inthe main scanning direction is controlled based on an encoder valueobtained by detecting a mark on an encoder sheet 14 by an encoder sensor13 arranged on the carriage 5.

The image forming apparatus 100 according to the embodiment includes amaintenance mechanism 15 for maintaining reliability of the recordinghead 6. The maintenance mechanism 15 cleans or caps the discharge faceof the recording head 6, and causes unnecessary ink to be ejected fromthe recording head 6.

As illustrated in FIG. 2, a platen 16 is arranged at a position oppositeto the discharge face of the recording head 6. The platen 16 supportsthe recording medium M when ink is discharged from the recording head 6onto the recording medium M. The image forming apparatus 100 accordingto the embodiment is a wide machine in which a moving distance of thecarriage 5 in the main scanning direction is long. Thus, the platen 16is configured by connecting a plurality of plate members in the mainscanning direction (moving direction of the carriage 5). The recordingmedium M is held by conveyance rollers driven by a sub-scanning motor(not illustrated) to be intermittently conveyed in a sub-scanningdirection (the arrow B direction in FIG. 2) on the platen 16.

The recording head 6 includes a plurality of nozzle arrays, and causesthe nozzle arrays to discharge ink onto the recording medium M conveyedon the platen 16 to form an image on the recording medium M. In theembodiment, to secure a large width of the image that can be formed onthe recording medium M through one scanning process performed by thecarriage 5, as illustrated in FIG. 3, the carriage 5 includes theupstream recording head 6 and the downstream recording head 6 mountedthereon. The number of recording heads 6 k that is mounted on thecarriage 5 and discharges black ink is two times the number of recordingheads 6 y, 6 m, and 6 c that discharge color ink. The recording heads 6y and 6 m are arranged separately on the left and the right. Thisarrangement causes overlapping orders of colors in the outward operationand the return operation of the carriage 5 to be identical to eachother, and prevents the colors from being changed between an outwardroute and a return route. The arrangement of the recording heads 6illustrated in FIG. 3 is merely an example, and the embodiment is notlimited thereto.

The components constituting the image forming apparatus 100 according tothe embodiment are arranged inside an exterior body 1. A covering member2 is provided to the exterior body 1 in an openable manner. Whenmaintenance of the image forming apparatus 100 is performed or a paperjam occurs, work can be conducted for the components arranged inside theexterior body 1 by opening the covering member 2.

The image forming apparatus 100 according to the embodiment includes anoperation panel 17 that displays various pieces of information andreceives an operation from a user. The operation panel 17 is connectedto a main control board (described later) arranged inside the exteriorbody 1 via a connecting cable (not illustrated).

The image forming apparatus 100 according to the embodimentintermittently conveys the recording medium M in the sub-scanningdirection on the platen 16, moves the carriage 5 in the main scanningdirection while the conveyance of the recording medium M in thesub-scanning direction is stopped, and causes the nozzle arrays of therecording head 6 mounted on the carriage 5 to discharge ink onto therecording medium M on the platen 16 to form an image on the recordingmedium M.

Specifically, when color adjustment is performed in the image formingapparatus 100, ink is discharged from the nozzle arrays of the recordinghead 6 mounted on the carriage 5 onto the recording medium M on theplaten 16 to form a large number of colorimetric patterns, andcolorimetry is performed on the colorimetric patterns. The colorimetricpattern is formed on the recording medium M by the image formingapparatus 100 actually using the ink, and reflects a characteristicspecific to the image forming apparatus 100. Accordingly, a deviceprofile describing the characteristic specific to the image formingapparatus 100 can be generated or modified using colorimetric values ofthe large number of colorimetric patterns. By performing colorconversion between a standard color space and a device-dependent colorbased on the device profile, the image forming apparatus 100 can outputan image with high reproducibility.

The image forming apparatus 100 according to the embodiment includes acolorimetric camera 20 having a function of capturing the image of thecolorimetric pattern formed on the recording medium M and calculatingthe colorimetric value. As illustrated in FIG. 2, the colorimetriccamera 20 is supported by the carriage 5 on which the recording head 6is mounted. The colorimetric camera 20 moves over the recording medium Mon which the colorimetric pattern is formed due to the conveyance of therecording medium M and the movement of the carriage 5. When reaching aposition opposite to the colorimetric pattern, the colorimetric camera20 captures the image. The colorimetric value of the colorimetricpattern is then calculated based on an RGB value of the colorimetricpattern obtained through the image capturing process.

The colorimetric camera 20 also has a function of identifying the typeof the recording medium M to be used in image formation in addition tothe function of calculating the colorimetric value of the colorimetricpattern. The image forming apparatus 100 according to the embodiment canperform optimum image formation on the recording medium M to be used, bydetermining, for example, a discharging type (a large droplet, a middledroplet, and a small droplet) of the ink discharged from the recordinghead 6 and resolution of the image to be formed on the recording mediumM according to the type of the recording medium M identified by thecolorimetric camera 20. A specific method of identifying the type of therecording medium M using the colorimetric camera 20 will be describedlater in detail.

Specific Example of Colorimetric Camera

Next, the following describes a specific example of the colorimetriccamera 20 in detail with reference to FIGS. 4A and 4B. FIGS. 4A and 4Bare diagrams illustrating a specific example of the colorimetric camera20. FIG. 4A is a vertical cross-sectional view of the colorimetriccamera 20, and FIG. 4B is a plan view of a bottom face 23 a of a housing23 of the colorimetric camera 20 viewed from the X1 direction in FIG.4A. In FIG. 4B, to clarify a positional relation between respectivecomponents arranged inside the colorimetric camera 20, positions where atwo-dimensional image sensor 26 and a first light source 31 (both aredescribed later) are projected onto the bottom face 23 a are indicatedby dashed lines.

The colorimetric camera 20 includes the housing 23 constructed bycombining a frame body 21 and a substrate 22. The frame body 21 isformed in a bottomed cylindrical shape which is opened at one end beingan upper surface of the housing 23. The substrate 22 is fastened to theframe body 21 with a fastening member and integrated with the frame body21 to close an open end of the frame body 21 and forms the upper surfaceof the housing 23.

The housing 23 is fixed to the carriage 5 so that the bottom face 23 athereof is opposite to the recording medium M on the platen 16 with apredetermined gap d therebetween. An opening 25 is provided to thebottom face 23 a of the housing 23 opposite to the recording medium M sothat an image of the recording medium M (the colorimetric pattern whenthe color adjustment is performed) can be captured from the inside ofthe housing 23.

The two-dimensional image sensor 26 for capturing the image is arrangedinside the housing 23. The two-dimensional image sensor 26 includes asensor chip 27 such as a CCD image capturing device or a CMOS imagecapturing device, and an imaging forming lens 28 that forms an opticalimage in an image capturing area of the two-dimensional image sensor 26on a sensor face of the sensor chip 27. The sensor chip 27 is mounted,for example, on a sensor substrate 24 supported by a supporting member(not illustrated) so that the sensor face thereof faces the bottom face23 a of the housing 23. The imaging forming lens 28 is fixed to thesensor chip 27 in a positioned state to keep a positional relation thatis determined according to optical characteristics of the imagingforming lens 28.

Another opening 29 is provided to the bottom face 23 a of the housing23, the opening 29 being adjacent to the opening 25 through which thetwo-dimensional image sensor 26 captures an image of a subject outsidethe housing 23. A reference chart 40 is arranged to close the opening 29from the outside of the housing 23, and held by a holding member 30. Theholding member 30 is attached to the housing 23 in a detachable manner.Accordingly, the reference chart 40 can be replaced by detaching theholding member 30 from the housing 23. An image of the reference chart40 is captured by the two-dimensional image sensor 26 together with thecolorimetric pattern to obtain a correct colorimetric value of thecolorimetric pattern.

The first light source 31 and a second light source 32 are arrangedinside the housing 23 as light sources for illuminating the imagecapturing area of the two-dimensional image sensor 26.

The first light source 31 is a light source that illuminates the imagecapturing area of the two-dimensional image sensor 26 almost uniformlywith diffused light, and is arranged so that specular reflection lightfrom the recording medium M outside the housing 23 and specularreflection light from the reference chart 40 inside the housing 23 arenot incident on the two-dimensional image sensor 26. In the embodiment,a light emitting diode (LED) mounted on an inner face of the substrate22 is used as the first light source 31. The first light source 31 isnot necessarily mounted on the substrate 22 directly. The first lightsource 31 may be arranged at a position where the specular reflectionlight from the recording medium M or the reference chart 40 can beprevented from being incident on the two-dimensional image sensor 26 andthe image capturing area of the two-dimensional image sensor 26 can bealmost uniformly illuminated. In the embodiment, the LED is used as thefirst light source 31, but the type of the light source is not limitedto the LED. For example, organic EL or the like may be used as the firstlight source 31. When the organic EL is used as the first light source31, illumination light close to a spectral distribution of sunlight canbe obtained, so that improvement in colorimetric accuracy is expected.

The second light source 32 is arranged so that the specular reflectionlight from the recording medium M outside the housing 23 is incident onthe two-dimensional image sensor 26. In the embodiment, an LED arrangedon a side wall of the frame body 21 positioned close to the opening 25is used as the second light source 32. The second light source 32 may bearranged so that the specular reflection light that is emitted from thesecond light source 32 and regularly reflected by the recording medium Moutside the housing 23 is incident on the two-dimensional image sensor26, and may be arranged at a position other than the side wall of theframe body 21. Similarly to the first light source 31, a light sourceother than the LED may be used as the second light source 32.

In identifying the type of the recording medium M (hereinafter, referredto as “in identifying the medium”), the colorimetric camera 20 accordingto the embodiment uses image data of a specular reflection region thatis a region in the image of the recording medium M captured by thetwo-dimensional image sensor 26 and reflects the specular reflectionlight from the recording medium M, and image data of a diffusedreflection region that reflects diffused reflection light from therecording medium M. The image data of the specular reflection region canbe acquired from the image of the recording medium M captured by thetwo-dimensional image sensor 26 under illumination of the second lightsource 32. The image data of the diffused reflection region may beacquired from the image of the recording medium M captured by thetwo-dimensional image sensor 26 under illumination of the second lightsource 32, or acquired from the image of the recording medium M capturedby the two-dimensional image sensor 26 under illumination of the firstlight source 31.

The mechanical configuration of the colorimetric camera 20 describedabove is merely an example, and the configuration is not limitedthereto. It is sufficient that the colorimetric camera 20 according tothe embodiment can at least perform colorimetry on the colorimetricpattern or identify the type of the recording medium M using the imagecaptured by the two-dimensional image sensor 26, and the configurationdescribed above can be variously changed or modified. Modifications ofthe colorimetric camera 20 will be described later in detail.

In the embodiment, the colorimetric camera 20 having a function ofperforming colorimetry on the colorimetric pattern is made to have afunction as a medium identification device that identifies the type ofthe recording medium M. Alternatively, the medium identification devicemay be implemented using an image capturing device other than thecolorimetric camera 20.

Schematic Configuration of Control Mechanism of Image Forming Apparatus

Next, the following describes a schematic configuration of a controlmechanism of the image forming apparatus 100 according to the embodimentwith reference to FIG. 5. FIG. 5 is a block diagram illustrating theschematic configuration of the control mechanism of the image formingapparatus 100.

The image forming apparatus 100 according to the embodiment includes, asillustrated in FIG. 5, a CPU 101, a ROM 102, a RAM 103, a recording headdriver 104, a main scanning driver 105, a sub-scanning driver 106, afield-programmable gate array (FPGA) for control 110, the recording head6, the colorimetric camera 20, the encoder sensor 13, the main scanningmotor 8, a sub-scanning motor 12, and the operation panel 17. The CPU101, the ROM 102, the RAM 103, the recording head driver 104, the mainscanning driver 105, the sub-scanning driver 106, and the FPGA forcontrol 110 are mounted on a main control board 120. The recording head6, the encoder sensor 13, and the colorimetric camera 20 are mounted onthe carriage 5 as described above.

The CPU 101 serves to totally control the image forming apparatus 100.For example, the CPU 101 executes various control programs stored in theROM 102 utilizing the RAM 103 as a working area, and outputs a controlcommand for controlling various operations in the image formingapparatus 100.

The recording head driver 104, the main scanning driver 105, and thesub-scanning driver 106 are drivers for driving the recording head 6,the main scanning motor 8, and the sub-scanning motor 12, respectively.

The FPGA for control 110 controls various operations in the imageforming apparatus 100 in cooperation with the CPU 101. The FPGA forcontrol 110 includes, for example, a CPU control unit 111, a memorycontrol unit 112, an ink discharge control unit 113, a sensor controlunit 114, a motor control unit 115, and a notification unit 116 asfunctional components.

The CPU control unit 111 communicates with the CPU 101 to transmitvarious pieces of information acquired by the FPGA for control 110 tothe CPU 101, and inputs the control command output from the CPU 101.

The memory control unit 112 performs memory control so that the CPU 101accesses the ROM 102 and the RAM 103.

The ink discharge control unit 113 controls the operation of therecording head driver 104 according to the control command from the CPU101 to control the operation of the recording head 6 driven by therecording head driver 104. In particular, according to the embodiment,the ink discharge control unit 113 determines the discharging type ofthe ink (a large droplet, a middle droplet, and a small droplet)discharged from the recording head 6 to the recording medium M and theresolution of the image to be formed on the recording medium M accordingto the type of the recording medium M identified by the colorimetriccamera 20, and controls the operation of the recording head 6 to performimage formation on the recording medium M with the determineddischarging type and resolution.

The sensor control unit 114 performs processing on a sensor signal suchas an encoder value output from the encoder sensor 13.

The motor control unit 115 controls the operation of the main scanningdriver 105 according to the control command from the CPU 101 to controlthe main scanning motor 8 driven by the main scanning driver 105, andcontrols movement of the carriage 5 in the main scanning direction. Themotor control unit 115 also controls the operation of the sub-scanningdriver 106 according to the control command from the CPU 101 to controlthe sub-scanning motor 12 driven by the sub-scanning driver 106, andcontrols movement of the recording medium M on the platen 16 in thesub-scanning direction.

The notification unit 116 causes, for example, the operation panel 17 todisplay a predetermined message when the colorimetric camera 20 cannotidentify the type of the recording medium M, and notifies a user usingthe image forming apparatus 100 that the type of the recording medium Mcannot be identified. A method of notification to the user is notlimited to display of the message by the operation panel 17. Forexample, a method of sounding a buzzer (not illustrated) may be used.

The components described above are merely an example of controlfunctions implemented by the FPGA for control 110. Various controlfunctions other than the above components may be implemented by the FPGAfor control 110. All or some of the control functions may be implementedby a computer program executed by the CPU 101 or another general-purposeCPU. Some of the control functions may be implemented by dedicatedhardware such as another FPGA different from the FPGA for control 110 oran application specific integrated circuit (ASIC).

The recording head 6 is driven by the recording head driver 104 theoperation of which is controlled by the CPU 101 and the FPGA for control110, and discharges the ink onto the recording medium M on the platen 16to form the image.

As described above, the colorimetric camera 20 captures, with thetwo-dimensional image sensor 26, an image of the colorimetric patternformed on the recording medium M under the illumination of the firstlight source 31 when color adjustment is performed in the image formingapparatus 100 together with an image of the reference chart 40, andcalculates the colorimetric value of the colorimetric pattern (a colorspecification value in a standard color space, for example, an L*a*b*value in an L*a*b* color space) based on the RGB value of thecolorimetric pattern obtained from the captured image and the RGB valueof each reference patch in the reference chart 40. The colorimetricvalue of the colorimetric pattern calculated by the colorimetric camera20 is transmitted to the CPU 101 via the FPGA for control 110. As aspecific method of calculating the colorimetric value of thecolorimetric pattern, a method disclosed in Japanese Patent ApplicationLaid-open No. 2013-051671 can be used, for example.

As described above, the colorimetric camera 20 captures, with thetwo-dimensional image sensor 26, the image of the recording medium Mbefore the image is formed (before the colorimetric pattern is formedwhen color adjustment is performed), and acquires image data of thespecular reflection region and image data of the diffused reflectionregion. Then, the colorimetric camera 20 uses the image data of thespecular reflection region and the image data of the diffused reflectionregion to identify the type of the recording medium M to be used forimage formation using a method described later. In the embodiment, it isassumed that the image data of the diffused reflection region isacquired from the image of the recording medium M captured by thetwo-dimensional image sensor 26 under the illumination of the firstlight source 31, and the image data of the specular reflection region isacquired from the image of the recording medium M captured by thetwo-dimensional image sensor 26 under the illumination of the secondlight source 32. That is, the two-dimensional image sensor 26 capturesan image two times to acquire the image data of the specular reflectionregion of the recording medium M and the image data of the diffusedreflection region thereof. Alternatively, both of the image data of thespecular reflection region and the image data of the diffused reflectionregion may be acquired from the image of the recording medium M capturedby the two-dimensional image sensor 26 under the illumination of thesecond light source 32. Medium information indicating the type of therecording medium M identified by the colorimetric camera 20 istransmitted to the ink discharge control unit 113 in the FPGA forcontrol 110. When the type of the recording medium M cannot beidentified, the medium information indicating that fact is transmittedfrom the colorimetric camera 20 to the notification unit 116 in the FPGAfor control 110.

The encoder sensor 13 outputs the encoder value obtained by detectingthe mark on the encoder sheet 14 to the FPGA for control 110. Theencoder value is transmitted from the FPGA for control 110 to the CPU101 and is used for calculating a position or speed of the carriage 5,for example. The CPU 101 generates and outputs a control command forcontrolling the main scanning motor 8 based on the position or the speedof the carriage 5 calculated from the encoder value.

Configuration of Control Mechanism of Colorimetric Camera

Next, the following specifically describes a control mechanism of thecolorimetric camera 20 with reference to FIG. 6. FIG. 6 is a blockdiagram illustrating a configuration example of the control mechanism ofthe colorimetric camera 20.

As illustrated in FIG. 6, the colorimetric camera 20 includes a timingsignal generating unit 41, a frame memory 42, an averaging processingunit 43, a colorimetric operation unit 44, a nonvolatile memory 45, alight source driving control unit 46, and an identifying unit 47 inaddition to the two-dimensional image sensor 26, the first light source31, and the second light source 32 described above.

The two-dimensional image sensor 26 converts the light incident on thetwo-dimensional image sensor 26 into an electric signal, and outputsimage data obtained by capturing an image of the image capturing area.The two-dimensional image sensor 26 incorporates a function of ADconverting an analog signal obtained through photoelectric conversioninto digital image data, and performing various pieces of imageprocessing such as shading correction, white balance correction, ycorrection, and format conversion on the image data to be output.Settings of various operation conditions for the two-dimensional imagesensor 26 are performed according to various setting signals from theCPU 101. Some or all of the various pieces of image processing on theimage data may be performed outside the two-dimensional image sensor 26.

The timing signal generating unit 41 generates a timing signal forcontrolling a timing for capturing an image with the two-dimensionalimage sensor 26, and supplies the timing signal to the two-dimensionalimage sensor 26. According to the embodiment, the two-dimensional imagesensor 26 captures an image not only in a case of performing colorimetryon the colorimetric pattern but also in a case of identifying the typeof the recording medium M used for image formation. The timing signalgenerating unit 41 generates the timing signal for controlling thetiming for starting capturing an image when the two-dimensional imagesensor 26 captures the image, and supplies the timing signal to thetwo-dimensional image sensor 26.

The frame memory 42 temporarily stores the image output from thetwo-dimensional image sensor 26.

In performing colorimetry on the colorimetric pattern, the averagingprocessing unit 43 extracts a colorimetric target region set near thecenter portion of a region reflecting the colorimetric pattern and aregion reflecting each reference patch of the reference chart 40 fromthe image that is output from the two-dimensional image sensor 26 andtemporarily stored in the frame memory 42. The averaging processing unit43 averages image data of the extracted colorimetric target region, andoutputs the obtained value to the colorimetric operation unit 44 as theRGB value of the colorimetric pattern. The averaging processing unit 43also averages image data of the region reflecting each reference patch,and outputs the obtained value to the colorimetric operation unit 44 asthe RGB of each reference patch.

The colorimetric operation unit 44 calculates the colorimetric value ofthe colorimetric pattern based on the RGB value of the colorimetricpattern obtained through the processing performed by the averagingprocessing unit 43 and the RGB value of each reference patch of thereference chart 40. The colorimetric value of the colorimetric patterncalculated by the colorimetric operation unit 44 is transmitted to theCPU 101 on the main control board 120. The colorimetric operation unit44 can calculate the colorimetric value of the colorimetric patternusing a method disclosed in Japanese Patent Application Laid-open No.2013-051671, for example, so that processing performed by thecolorimetric operation unit 44 will not be described in detail herein.

The nonvolatile memory 45 stores various pieces of data required forcalculating the colorimetric value of the colorimetric pattern by thecolorimetric operation unit 44, and various pieces of informationreferred to by the identifying unit 47 in identifying the medium.

The light source driving control unit 46 generates a light sourcedriving signal for driving the first light source 31 or the second lightsource 32 to be supplied to the first light source 31 and the secondlight source 32. As described above, the colorimetric camera 20according to the embodiment captures an image with the two-dimensionalimage sensor 26 under the illumination of the first light source 31 inperforming colorimetry on the colorimetric pattern, and captures animage with the two-dimensional image sensor 26 under the illumination ofthe first light source 31 while capturing an image with thetwo-dimensional image sensor 26 under the illumination of the secondlight source 32 in identifying the medium. Accordingly, the light sourcedriving control unit 46 supplies the light source driving signal to thefirst light source 31 in synchronization with a timing for capturing animage by the two-dimensional image sensor 26 in performing colorimetryon the colorimetric pattern, and sequentially supplies light sourcedriving signals to the first light source 31 and the second light source32 in synchronization with two timings for capturing an image by thetwo-dimensional image sensor 26 in identifying the medium.

The identifying unit 47 identifies the type of the recording medium Musing the image of the recording medium M captured by thetwo-dimensional image sensor 26. Specifically, the identifying unit 47first acquires, from the image of the recording medium M captured by thetwo-dimensional image sensor 26, the image data of the specularreflection region reflecting the specular reflection light from therecording medium M and the image data of the diffused reflection regionreflecting the diffused reflection light from the recording medium M.The image data of the specular reflection region can be acquired byextracting the specular reflection region that is specified inaccordance with a positional relation between the second light source 32and the two-dimensional image sensor 26 from the image of the recordingmedium M captured by the two-dimensional image sensor 26 under theillumination of the second light source 32. The image data of thediffused reflection region can be acquired by extracting a predeterminedregion from the image of the recording medium M captured by thetwo-dimensional image sensor 26 under the illumination of the firstlight source 31. The image data of the diffused reflection region may beacquired by extracting an arbitrary region other than the specularreflection region from the image of the recording medium M captured bythe two-dimensional image sensor 26 under the illumination of the secondlight source 32.

The identifying unit 47 obtains a glossiness evaluation value indicatingglossiness of the recording medium M, a surface roughness evaluationvalue indicating surface roughness of the recording medium M, and acoloring evaluation value indicating coloring of the recording medium Musing the image data of the specular reflection region and the imagedata of the diffused reflection region that are acquired as describedabove. The identifying unit 47 then identifies the type of the recordingmedium M by combining determination using the glossiness evaluationvalue, determination using the surface roughness evaluation value, anddetermination using the coloring evaluation value.

It is assumed that the identifying unit 47 according to the embodimentobtains, as the glossiness evaluation value, a peak value of a luminancehistogram of the specular reflection region, and a value of a standarddeviation σ of a histogram of a residual that is a difference between aluminance distribution in the specular reflection region and a normaldistribution. In this case, the determination using the glossinessevaluation value includes processing of threshold determination of apeak value (a luminance value the frequency of which is the largest) ofthe luminance histogram of the specular reflection region, andprocessing of threshold comparison of the value of the standarddeviation σ of the histogram of the residual that is a differencebetween the luminance distribution in the specular reflection region andthe normal distribution. Hereinafter, the former processing is called“specular reflection histogram data analysis”, and the latter processingis called “specular reflection residual histogram data analysis”.

The identifying unit 47 according to the embodiment obtains, forexample, the value of the standard deviation σ of the luminancehistogram of the diffused reflection region as the surface roughnessevaluation value. In this case, the determination using the surfaceroughness evaluation value is processing of threshold comparison of thevalue of the standard deviation σ of the luminance histogram of thediffused reflection region. Hereinafter, the above processing is called“diffused reflection histogram data analysis”.

The identifying unit 47 according to the embodiment obtains, forexample, a coordinate value of when the RGB value of the pixel includedin the diffused reflection region is plotted in an RGB color space asthe coloring evaluation value. In this case, the determination using thecoloring evaluation value is processing of collating the coordinatevalue of when the RGB value of the pixel included in the diffusedreflection region is plotted in the RGB color space with a coordinaterange in the RGB color space set for each type of the registeredrecording medium M. Hereinafter, the above processing is called“diffused reflection RGB data analysis”.

The identifying unit 47 according to the embodiment identifies the typeof the recording medium M used for image formation by combining the“specular reflection histogram data analysis”, the “specular reflectionresidual histogram data analysis”, the “diffused reflection histogramdata analysis”, and the “diffused reflection RGB data analysis”described above. The following describes a specific example ofprocessing performed by the identifying unit 47 in detail exemplifying acase of identifying which one of nine types of recording media including“glossy paper”, “plain paper”, “mat coated paper”, “semi-glossy paper”,“coated paper”, “tracing paper”, a “mat film”, “inkjet plain paper”, and“recycled paper” is used as the recording medium M for image formation.

Overview of Operation of Colorimetric Camera in Identifying Medium

The following describes an overview of an operation of the colorimetriccamera 20 in identifying the medium with reference to FIG. 7. FIG. 7 isa flowchart illustrating an operation procedure of the colorimetriccamera 20 in identifying the medium.

In identifying the medium, first, the image of the recording medium M iscaptured by the two-dimensional image sensor 26 under the illuminationof the second light source (Step S101). The image of the recordingmedium M captured by the two-dimensional image sensor 26 is stored inthe frame memory 42. The identifying unit 47 then extracts apredetermined region from the image of the recording medium M stored inthe frame memory 42 to acquire the image data of the specular reflectionregion (Step S102).

Next, the image of the recording medium M is captured by thetwo-dimensional image sensor 26 under the illumination of the firstlight source 31 (Step S103). The image of the recording medium Mcaptured by the two-dimensional image sensor 26 is stored in the framememory 42. The identifying unit 47 then extracts a predetermined regionfrom the image of the recording medium M stored in the frame memory 42to acquire the image data of the diffused reflection region (Step S104).The order of the image capturing at Step S101 and the image capturing atStep S103 may be reversed. The image data of the specular reflectionregion and the image data of the diffused reflection region may beacquired after the image capturing at Step S101 and the image capturingat Step S103 are sequentially performed.

Next, the identifying unit 47 performs processing of identifying thetype of the recording medium M based on the image data of the specularreflection region acquired at Step S102 and the image data of thediffused reflection region acquired at Step S104 (Step S105). Theprocessing at Step S105 is processing combining the “specular reflectionhistogram data analysis”, the “specular reflection residual histogramdata analysis”, the “diffused reflection histogram data analysis”, andthe “diffused reflection RGB data analysis” described above.

If the type of the recording medium M can be identified through theprocessing at Step S105 (Yes at Step S106), the colorimetric camera 20transmits medium information indicating the identified type of therecording medium M to the FPGA for control 110 on the main control board120 (Step S107). On the other hand, if the type of the recording mediumM cannot be identified through the processing at Step S105 (No at StepS106), the colorimetric camera 20 transmits medium informationindicating that the type of the recording medium M cannot be identifiedto the FPGA for control 110 on the main control board 120 (Step S108).

The following describes details about the processing at Step S105 withspecific examples.

Specular Reflection Histogram Data Analysis

First, the following describes the “specular reflection histogram dataanalysis”. As described above, the “specular reflection histogram dataanalysis” is processing of threshold determination of the peak value ofthe luminance histogram of the specular reflection region.

FIGS. 8A and 8B are diagrams illustrating an example of the image of therecording medium M captured by the two-dimensional image sensor 26 underthe illumination of the second light source 32. FIG. 8A illustrates anexample of the entire image of the recording medium M captured throughthe opening 25 of the housing 23. FIG. 8B illustrates an example of theimage of the specular reflection region extracted from the example ofthe image in FIG. 8A. A position of the specular reflection regionexemplified in FIG. 8B can be specified based on a positional relationbetween the second light source 32 and the two-dimensional image sensor26. Accordingly, the identifying unit 47 can acquire the image data ofthe specular reflection region by extracting the image of the specularreflection region exemplified in FIG. 8B from the image exemplified inFIG. 8A.

In the “specular reflection histogram data analysis”, the identifyingunit 47 generates a luminance histogram from the image data of thespecular reflection region illustrated in FIG. 8B. The luminancehistogram represents a relation between a luminance value of the pixelincluded in the image and the frequency thereof (the number of pixelshaving the same luminance value). In the colorimetric camera 20according to the embodiment, three types (R, G, and B) of luminancevalues can be acquired for each pixel because the two-dimensional imagesensor 26 outputs RGB image data. However, only one of the luminancevalues may be used because the luminance values have similar tendency.In the embodiment, a luminance value of G (for example, 256 valuesrepresented by 8 bits) is used. The luminance value slightly variesdepending on a surface shape of the platen 16 that supports therecording medium M when the two-dimensional image sensor 26 captures animage, but the variation is negligible. In the embodiment, it is assumedthat the two-dimensional image sensor 26 captures an image of a portionof the recording medium M supported by the platen 16, the portion beingpositioned on a flat part (also referred to as a lateral rib part) otherthan a recessed part or a hole of the platen 16.

FIG. 9 is a diagram illustrating an example of the luminance histogramof the specular reflection region in which a horizontal axis representsthe luminance value of the pixel (in the embodiment, 256 values of G),and a vertical axis represents the frequency. The identifying unit 47generates the luminance histogram exemplified in FIG. 9 from the imagedata of the specular reflection region, and detects the peak value ofthe luminance histogram to perform threshold comparison. In this case,the peak value of the luminance histogram means the luminance value thefrequency of which is the largest. The luminance histogram illustratedin FIG. 9 is an example of a case in which the type of the recordingmedium M is “glossy paper”, and the peak value of the luminancehistogram (the luminance value the frequency of which is the largest) is“210”.

FIG. 10 is a diagram illustrating a relation between the types of therecording media M and the peak value of the luminance histogram of thespecular reflection region. When the peak value of the luminancehistogram of the specular reflection region is detected for each of thenine types of recording media M described above, as illustrated in FIG.10, a large value exceeding “200” is detected for the “glossy paper”,and a small value such as about “50” is detected for each of the“tracing paper” and the “mat film”. For each of the “plain paper”, the“mat coated paper”, the “semi-glossy paper”, the “coated paper”, the“inkjet plain paper”, and the “recycled paper” other than the above, thepeak values of the luminance histogram are detected in a range from“100” to “150”. Accordingly, as illustrated in FIG. 10, for example, theidentifying unit 47 sets a first threshold Th1 between “150” and “200”and sets a second threshold Th2 between “50” and “100”, and compares thepeak value of the luminance histogram obtained from the image data ofthe specular reflection region with the first threshold Th1 and thesecond threshold Th2 to identify whether the recording medium M is the“glossy paper”, the “tracing paper”, or the “mat film”, or the othertypes.

That is, when the peak value of the luminance histogram obtained fromthe image data of the specular reflection region is larger than thefirst threshold Th1, the recording medium M can be determined to be the“glossy paper”. When the peak value of the luminance histogram obtainedfrom the image data of the specular reflection region is smaller thanthe second threshold Th2, the recording medium M can be determined to bethe “tracing paper” or the “mat film”. When the peak value of theluminance histogram obtained from the image data of the specularreflection region is between the first threshold Th1 and the secondthreshold Th2, the recording medium M can be determined to be any of the“plain paper”, the “mat coated paper”, the “semi-glossy paper”, the“coated paper”, the “inkjet plain paper”, and the “recycled paper”.Appropriate values for the first threshold Th1 and the second thresholdTh2 are determined in advance and stored in the nonvolatile memory 45.In performing “specular reflection histogram data analysis”, theidentifying unit 47 reads out the first threshold Th1 and the secondthreshold Th2 from the nonvolatile memory 45 and set the first thresholdTh1 and the second threshold Th2 as comparison targets of the peak valueof the luminance histogram obtained from the image data of the specularreflection region. Information indicating a relation between the firstthreshold Th1 and the second threshold Th2, and the peak value of theluminance histogram of the specular reflection region (whether the peakvalue is larger or smaller than the threshold) is stored, for example,in the nonvolatile memory 45 in a format that can be referred to foreach of the registered recording media M.

Diffused Reflection Histogram Data Analysis

Next, the following describes the “diffused reflection histogram dataanalysis”. As described above, the “diffused reflection histogram dataanalysis” is processing of threshold comparison of the value of thestandard deviation σ of the luminance histogram of the diffusedreflection region.

In the “diffused reflection histogram data analysis”, the identifyingunit 47 generates the luminance histogram from the image data of thediffused reflection region. FIG. 11 is a diagram three-dimensionallyillustrating the luminance distribution in the diffused reflectionregion in a case in which the recording medium M is the “mat film” inwhich each of two axes in the horizontal direction represents theposition of the pixel in the diffused reflection region, and an axis inthe vertical direction represents the luminance value of each pixel (inthe embodiment, 256 values of G). FIG. 12 is a diagram illustrating anexample of the luminance histogram of the diffused reflection region ina case in which the recording medium M is the “mat film”. Theidentifying unit 47 generates the luminance histogram as illustrated inFIG. 12 from the image data of the diffused reflection region, andobtains the value of the standard deviation σ thereof. In the luminancehistogram illustrated in FIG. 12, a value of an average ave is “55.8”and the value of the standard deviation σ is “1.59”.

FIG. 13 is a diagram three-dimensionally illustrating the luminancedistribution in the diffused reflection region in a case in which therecording medium M is the “tracing paper” in which each of two axes inthe horizontal direction represents the position of the pixel in thediffused reflection region, and an axis in the vertical directionrepresents the luminance value of each pixel (in the embodiment, 256values of G). FIG. 14 is a diagram illustrating an example of theluminance histogram of the diffused reflection region in a case in whichthe recording medium M is the “tracing paper”. The identifying unit 47generates the luminance histogram as illustrated in FIG. 14 from theimage data of the diffused reflection region, and obtains the value ofthe standard deviation σ thereof. In the luminance histogram illustratedin FIG. 14, the value of the average ave is “52.0” and the value of thestandard deviation σ is “3.75”.

FIG. 15 is a diagram illustrating a relation between the types of therecording media M and the value of the standard deviation σ of theluminance histogram of the diffused reflection region. When the value ofthe standard deviation σ of the luminance histogram of the diffusedreflection region is obtained for each of the nine types of recordingmedia M described above, as illustrated in FIG. 15, a large value closeto “4” is calculated for the “tracing paper”, and a relatively smallvalue in a range from “1” to “2” is calculated for each of the “glossypaper”, the “plain paper”, the “mat coated paper”, the “semi-glossypaper”, the “coated paper”, the “mat film”, the “inkjet plain paper”,and the “recycled paper” other than the above. Accordingly, asillustrated in FIG. 15 for example, the identifying unit 47 sets a thirdthreshold Th3 between “2” and “3”, and compares the value of thestandard deviation σ of the luminance histogram obtained from the imagedata of the diffused reflection region with the third threshold Th3 toidentify whether the recording medium M is the “tracing paper” or theother types.

That is, when the value of the standard deviation σ of the luminancehistogram obtained from the image data of the diffused reflection regionis larger than the third threshold Th3, the recording medium M can bedetermined to be the “tracing paper”. In a case in which the “diffusedreflection histogram data analysis” is performed after the recordingmedium M is determined to be the “tracing paper” or the “mat film”through the “specular reflection histogram data analysis” describedabove, when the value of the standard deviation σ of the luminancehistogram obtained from the image data of the diffused reflection regionis smaller than the third threshold Th3, the recording medium M can bedetermined to be the “mat film”. An appropriate value for the thirdthreshold Th3 is determined in advance and stored in the nonvolatilememory 45. In performing “diffused reflection histogram data analysis”,the identifying unit 47 reads out the third threshold Th3 from thenonvolatile memory 45 and sets he third threshold Th3 as a comparisontarget of the value of the standard deviation σ of the luminancehistogram obtained from the image data of the diffused reflectionregion. Information indicating a relation between the third thresholdTh3 and the value of the standard deviation σ of the luminance histogramof the diffused reflection region (whether the value is larger orsmaller than the threshold) is stored, for example, in the nonvolatilememory 45 in a format that can be referred to for each of the registeredrecording media M.

Specular Reflection Residual Histogram Data Analysis

Next, the following describes the “specular reflection residualhistogram data analysis”. As described above, the “specular reflectionresidual histogram data analysis” is processing of threshold comparisonof the value of the standard deviation σ of the histogram of theresidual that is a difference between the luminance distribution in thespecular reflection region and the normal distribution.

In the “specular reflection residual histogram data analysis”, theidentifying unit 47 generates the histogram of the residual that is adifference between the luminance distribution in the specular reflectionregion and the normal distribution from the image data of the specularreflection region. FIG. 16 is a diagram three-dimensionally illustratingthe luminance distribution in the specular reflection region in a casein which the recording medium M is the “semi-glossy paper”. FIG. 17 is adiagram three-dimensionally illustrating a residual distribution. InFIGS. 16 and 17, each of two axes in the horizontal direction representsthe position of the pixel in the specular reflection region. In FIG. 16,an axis in the vertical direction represents the luminance value of eachpixel (in the embodiment, 256 values of G). In FIG. 17, an axis in thevertical direction represents a residual value of each pixel. FIG. 18 isa diagram illustrating an example of the histogram of the residual in acase in which the recording medium M is the “semi-glossy paper”. Thehistogram of the residual represents a relation between the residualvalue of each pixel and the frequency thereof (the number of pixelshaving the same residual value) in the specular reflection region. Theidentifying unit 47 generates the histogram of the residual asillustrated in FIG. 18 from the image data of the specular reflectionregion, and obtains the value of the standard deviation σ thereof. Inthe histogram of the residual illustrated in FIG. 18, the value of thestandard deviation σ is “15.0”.

FIG. 19 is a diagram illustrating a relation between the types of therecording media M and the value of the standard deviation σ of thehistogram of the residual of the specular reflection region. When thevalue of the standard deviation σ of the histogram of the residual ofthe specular reflection region is obtained for each of the nine types ofrecording media M described above, as illustrated in FIG. 19, relativelylarge values such as “10” for the “glossy paper” and “15” for the“semi-glossy paper” are calculated, and a relatively small value equalto or smaller than “5” is calculated for the “plain paper”, the “matcoated paper”, the “coated paper”, the “tracing paper”, the “mat film”,the “inkjet plain paper”, and the “recycled paper” other than the above.Accordingly, as illustrated in FIG. 19, for example, the identifyingunit 47 sets a fourth threshold Th4 between “5” and “10”, and comparesthe value of the standard deviation σ of the histogram of the residualobtained from the image data of the specular reflection region with thefourth threshold Th4 to identify whether the recording medium M is the“glossy paper” or the “semi-glossy paper”, or other types.

That is, when the value of the standard deviation σ of the histogram ofthe residual obtained from the image data of the specular reflectionregion is larger than the fourth threshold Th4, the recording medium Mcan be determined to be the “glossy paper” or the “semi-glossy paper”.In a case in which the “specular reflection residual histogram dataanalysis” is performed after the recording medium M is determined to beany of the “plain paper”, the “mat coated paper”, the “semi-glossypaper”, the “coated paper”, the “inkjet plain paper”, and the “recycledpaper” through the “specular reflection histogram data analysis”described above, when the value of the standard deviation σ of thehistogram of the residual obtained from the image data of the specularreflection region is larger than the fourth threshold Th4, the recordingmedium M can be determined to be the “semi-glossy paper”. An appropriatevalue for the fourth threshold Th4 is determined in advance and storedin the nonvolatile memory 45. In performing “specular reflectionresidual histogram data analysis”, the identifying unit 47 reads out thefourth threshold Th4 from the nonvolatile memory 45 and sets the fourththreshold Th4 as a comparison target of the value of the standarddeviation σ of the histogram of the residual obtained from the imagedata of the specular reflection region. Information indicating arelation between the fourth threshold Th4 and the value of the standarddeviation σ of the histogram of the residual (whether the value islarger or smaller than the threshold) is stored, for example, in thenonvolatile memory 45 in a format that can be referred to for each ofthe registered recording media M.

Diffused Reflection RGB Data Analysis

Next, the following describes the “diffused reflection RGB dataanalysis”. As described above, the “diffused reflection RGB dataanalysis” is processing of collating the coordinate value of when theRGB value of the pixel included in the diffused reflection region isplotted in the RGB color space, with the coordinate range in the RGBcolor space set for each type of the registered recording medium M.

In the “diffused reflection RGB data analysis”, the identifying unit 47extracts the RGB value of an arbitrary pixel from the image data of thediffused reflection region. The RGB value extracted herein may be an RGBvalue of a specified pixel included in the diffused reflection region,an average value of RGB values of a plurality of specified pixels, or anaverage value of RGB values of all the pixels included in the diffusedreflection region. The identifying unit 47 then identifies the type ofthe recording medium M by determining the type of the recording medium Mto which a coordinate range among coordinate ranges set in the RGB colorspace corresponds, the coordinate range including the coordinate valueof when the extracted RGB value is plotted in the RGB color space.

FIGS. 20A to 20D are diagrams illustrating the coordinate range in theRGB color space that is set for each type of the registered recordingmedium M. FIG. 20A illustrates the coordinate range in the RGB colorspace of the “plain paper”, the “mat coated paper”, the “coated paper”,the “inkjet plain paper”, and the “recycled paper” among the types ofthe registered recording media M, FIG. 20B illustrates a projection onan R-G plane, FIG. 20C illustrates a projection on a G-B plane, and FIG.20D illustrates a projection on an R-B plane.

Each coordinate range illustrated in FIG. 20 is, for example, set asfollows. That is, an image of each recording medium M is captured by thetwo-dimensional image sensor 26 a certain number of times (for example,thirty times) under the illumination of the first light source 31 inadvance. The RGB value is extracted from each of the certain number ofpieces of the obtained image data of the diffused reflection region, anda range of 2σ of a distribution thereof is obtained and stored in thenonvolatile memory 45. In performing “diffused reflection RGB dataanalysis”, the identifying unit 47 reads out, from the nonvolatilememory 45, the range of 2σ obtained in advance for each type of therecording medium M to be set in the RGB color space. The identifyingunit 47 then identifies the type of the recording medium M bydetermining the coordinate range set in the RGB color space in which theRGB value extracted from the image data of the diffused reflectionregion is included.

Among the nine types of recording media M described in this embodiment,five types including the “plain paper”, the “mat coated paper”, the“coated paper”, the “inkjet plain paper”, and the “recycled paper”cannot be uniquely identified through the “specular reflection histogramdata analysis”, the “diffused reflection histogram data analysis”, andthe “specular reflection residual histogram data analysis” describedabove. However, respective coordinate ranges in the RGB color spacecorresponding to the “plain paper”, the “mat coated paper”, the “coatedpaper”, the “inkjet plain paper”, and the “recycled paper” do notinterfere with each other, and are separated from each other in the RGBcolor space, so that these types can be identified through the “diffusedreflection RGB data analysis”.

The colorimetric camera 20 according to the embodiment includes thecolorimetric operation unit 44 that converts the RGB value into thecolorimetric value such as the L*a*b* value. Accordingly, theidentifying unit 47 can perform processing similar to the “diffusedreflection RGB data analysis” using the Lab value in place of the RGBvalue. Hereinafter, this processing is called “diffused reflectionL*a*b* data analysis”.

Diffused Reflection L*a*b* Data Analysis

The “diffused reflection L*a*b* data analysis” is processing ofcollating a coordinate value of when the L*a*b* value of the pixelincluded in the diffused reflection region is plotted in the L*a*b*color space with a coordinate range in the L*a*b* color space that isset for each type of the registered recording medium M.

In the “diffused reflection L*a*b* data analysis”, the identifying unit47 extracts the RGB value of an arbitrary pixel from the image data ofthe diffused reflection region. The value extracted herein may be an RGBvalue of a specified pixel included in the diffused reflection region,an average value of RGB values of a plurality of specified pixels, or anaverage value of RGB values of all the pixels included in the diffusedreflection region. The identifying unit 47 then passes the extracted RGBvalue to the colorimetric operation unit 44, requests the colorimetricoperation unit 44 to convert the RGB value into the L*a*b* value, andacquires, from the colorimetric operation unit 44, the L*a*b* valueconverted from the RGB value. The identifying unit 47 then identifiesthe type of the recording medium M by determining the type of therecording medium M to which a coordinate range among coordinate rangesset in the L*a*b* color space corresponds, the coordinate rangeincluding the coordinate value of when the acquired L*a*b* value isplotted in the L*a*b* color space.

FIGS. 21A to 21D are diagrams illustrating a coordinate range in theL*a*b* color space that is set for each type of the registered recordingmedium M. FIG. 21A illustrates the coordinate range in the L*a*b* colorspace of the “plain paper”, the “mat coated paper”, the “coated paper”,the “inkjet plain paper”, and the “recycled paper” among the types ofthe registered recording media M, FIG. 21B illustrates a projection onan a*-b* plane, FIG. 21C illustrates a projection on a b*-L* plane, andFIG. 21D illustrates a projection on an a*-L* plane.

Each coordinate range illustrated in FIG. 21 is, for example, set asfollows. That is, an image of each recording medium M is captured by thetwo-dimensional image sensor 26 a certain number of times (for example,thirty times) under the illumination of the first light source 31 inadvance. The RGB value is extracted from each of the certain number ofpieces of the obtained image data of the diffused reflection region andconverted into the L*a*b* value. Then, a range of 2σ of a distributionthereof is obtained and stored in the nonvolatile memory 45. Inperforming “diffused reflection L*a*b* data analysis”, the identifyingunit 47 reads out, from the nonvolatile memory 45, the range of 2σobtained in advance for each type of the recording medium M to be set inthe L*a*b* color space. The identifying unit 47 then identifies the typeof the recording medium M by determining the coordinate range set in theL*a*b* color space in which the L*a*b* value converted from the RGBvalue that is extracted from the image data of the diffused reflectionregion is included.

Among the nine types of recording media M described in this embodiment,five types including the “plain paper”, the “mat coated paper”, the“coated paper”, the “inkjet plain paper”, and the “recycled paper”cannot be uniquely identified through the “specular reflection histogramdata analysis”, the “diffused reflection histogram data analysis”, andthe “specular reflection residual histogram data analysis” describedabove. However, respective coordinate ranges in the L*a*b* color spacecorresponding to the “plain paper”, the “mat coated paper”, the “coatedpaper”, the “inkjet plain paper”, and the “recycled paper” do notinterfere with each other, and are separated from each other in theL*a*b* color space, so that these types can be identified through the“diffused reflection L*a*b* data analysis”.

Specific Example of Processing Procedure of Identifying Unit

Next, the following describes a specific example of a processingprocedure (the processing procedure at Step S105 in FIG. 7) performed bythe identifying unit 47 with reference to FIG. 22. FIG. 22 is aflowchart illustrating an example of the processing procedure performedby the identifying unit 47.

The identifying unit 47 first performs “specular reflection histogramdata analysis” (Step S201), and determines whether the peak value of theluminance histogram obtained from the image data of the specularreflection region is larger than the first threshold Th1 (Step S202). Ifthe peak value is larger than the first threshold Th1 (Yes at StepS202), the identifying unit 47 determines that the recording medium M isthe “glossy paper” (Step S203), and ends the processing.

On the other hand, if the peak value of the luminance histogram obtainedfrom the image data of the specular reflection region is equal to orsmaller than the first threshold Th1 (No at Step S202), the identifyingunit 47 determines whether the peak value is smaller than the secondthreshold Th2 (Step S204). If the peak value is smaller than the secondthreshold Th2 (Yes at Step S204), the identifying unit 47 then performs“diffused reflection histogram data analysis” (Step S205), anddetermines whether the value of the standard deviation σ of theluminance histogram obtained from the image data of the diffusedreflection region is larger than the third threshold Th3 (Step S206). Ifthe value of the standard deviation σ is larger than the third thresholdTh3 (Yes at Step S206), the identifying unit 47 determines that therecording medium M is the “tracing paper” (Step S207), and ends theprocessing. On the other hand, if the value of the standard deviation σis equal to or smaller than the third threshold Th3 (No at Step S206),the identifying unit 47 determines that the recording medium M is the“mat film” (Step S208), and ends the processing.

On the other hand, at the determination at Step S204, if the peak valueof the luminance histogram obtained from the image data of the specularreflection region is equal to or larger than the second threshold Th2(No at Step S204), the identifying unit 47 then performs “specularreflection residual histogram data analysis” (Step S209), and determineswhether the value of the standard deviation σ of the histogram of theresidual obtained from the image data of the specular reflection regionis larger than the fourth threshold Th4 (Step S210). If the value of thestandard deviation σ of the histogram of the residual is larger than thefourth threshold Th4 (Yes at Step S210), the identifying unit 47determines that the recording medium M is the “semi-glossy paper” (StepS211), and ends the processing.

On the other hand, if the value of the standard deviation σ of thehistogram of the residual is equal to or smaller than the fourththreshold Th4 (No at Step S210), the identifying unit 47 then performs“diffused reflection RGB data analysis” (Step S212), and determines thetype of the recording medium M to which a coordinate range amongcoordinate ranges set in the RGB color space corresponds, the coordinaterange including the coordinate value of when the RGB value extractedfrom the image data of the diffused reflection region is plotted in theRGB color space. If the coordinate value is included in the coordinaterange corresponding to the “plain paper” (Yes at Step S213), theidentifying unit 47 determines that the recording medium M is the “plainpaper” (Step S214), and ends the processing. If the coordinate value isincluded in the coordinate range corresponding to the “recycled paper”(Yes at Step S215), the identifying unit 47 determines that therecording medium M is the “recycled paper” (Step S216), and ends theprocessing. If the coordinate value is included in the coordinate rangecorresponding to the “inkjet plain paper” (Yes at Step S217), theidentifying unit 47 determines that the recording medium M is the“inkjet plain paper” (Step S218), and ends the processing. If thecoordinate value is included in the coordinate range corresponding tothe “mat coated paper” (Yes at Step S219), the identifying unit 47determines that the recording medium M is the “mat coated paper” (StepS220), and ends the processing. If the coordinate value is included inthe coordinate range corresponding to the “coated paper” (Yes at StepS221), the identifying unit 47 determines that the recording medium M isthe “coated paper” (Step S222), and ends the processing. If thecoordinate value is not included in any of the coordinate ranges (No atStep S213, No at Step S215, No at Step S217, No at Step S219, and No atStep S221), the identifying unit 47 determines that the type of therecording medium M cannot be identified (Step S223), and ends theprocessing.

FIG. 23 is a diagram for explaining a relation between an example of theprocessing procedure performed by the identifying unit 47 andidentification results in a case in which the processing is performed inthe order of the “specular reflection histogram data analysis”, the“diffused reflection histogram data analysis”, the “specular reflectionresidual histogram data analysis”, and the “diffused reflection RGB dataanalysis”.

Through the “specular reflection histogram data analysis”, the types ofthe recording media M can be classified into three, that is, A1, B1, andC1 illustrated in FIG. 23. The recording medium M classified as A1 isonly the “glossy paper”. Accordingly, when the recording medium M is the“glossy paper”, the identification process is ended at this phase.

Next, through the “diffused reflection histogram data analysis”, thetypes of the recording media M can be classified into two, that is, A2and B2 illustrated in FIG. 23. The recording medium M classified as A2is only the “tracing paper”. Accordingly, when the recording medium M isthe “tracing paper”, the identification process is ended at this phase.Among the recording media M classified as B2, the recording medium Mclassified as B1 through the above “specular reflection histogram dataanalysis” is only the “mat film”. Accordingly, when the recording mediumM is the “mat film”, the identification process is ended at this phase.

Next, through the “specular reflection residual histogram dataanalysis”, the types of the recording media M can be classified intotwo, that is, A3 and B3 illustrated in FIG. 23. The recording medium Mclassified as A3 is only the “glossy paper” and the “semi-glossy paper”,and the “glossy paper” is identified through the above “specularreflection histogram data analysis”. Accordingly, when the recordingmedium M is the “semi-glossy paper”, the identification process is endedat this phase.

Next, through the “diffused reflection RGB data analysis”, the fivetypes (A4, B4, C4, D4, and E4 illustrated in FIG. 23) that have not beenidentified can be identified. When the recording medium M is any of the“plain paper”, the “recycled paper”, the “inkjet plain paper”, the “matcoated paper”, and the “coated paper”, the identification process isended at this phase.

The order of the processing procedure performed by the identifying unit47 is not limited to the example described above. For example, the“specular reflection residual histogram data analysis” may be performedfirst. FIG. 24 illustrates an example of a case in which the identifyingunit 47 performs the processing in the order of the “specular reflectionresidual histogram data analysis”, the “specular reflection histogramdata analysis”, the “diffused reflection histogram data analysis”, andthe “diffused reflection RGB data analysis”.

In this case, first, the types of the recording media M may beclassified into two types, that is, A1 and B1 illustrated in FIG. 24through the “specular reflection residual histogram data analysis”.

Next, the types of the recording media M can be classified into threetypes, that is, A2, B2, and C2 illustrated in FIG. 24 through the“specular reflection histogram data analysis”. The recording medium Mclassified as A2 is only the “glossy paper”. Accordingly, when therecording medium M is the “glossy paper”, the identification process isended at this phase. Among the recording media M classified as C2, therecording medium M classified as A1 through the above “specularreflection residual histogram data analysis” is only the “semi-glossypaper”. Accordingly, when the recording medium M is the “semi-glossypaper”, the identification process is ended at this phase.

Next, through the “diffused reflection histogram data analysis”, thetypes of the recording media M can be classified into two types, thatis, A3 and B3 illustrated in FIG. 24. The recording medium M classifiedas A3 is only the “tracing paper”. Accordingly, when the recordingmedium M is the “tracing paper”, the identification process is ended atthis phase. Among the recording media M classified as B3, the recordingmedium M classified as B2 through the above “specular reflectionhistogram data analysis” is only the “mat film”. Accordingly, when therecording medium M is the “mat film”, the identification process isended at this phase.

Next, through the “diffused reflection RGB data analysis”, the fivetypes (A4, B4, C4, D4, and E4 illustrated in FIG. 24) that have not beenidentified can be identified. When the recording medium M is any of the“plain paper”, the “recycled paper”, the “inkjet plain paper”, the “matcoated paper”, and the “coated paper”, the identification process isended at this phase.

When the identifying unit 47 identifies the type of the recording mediumM as described above, medium information indicating the type of therecording medium M is transmitted from the colorimetric camera 20 to theink discharge control unit 113 in the FPGA for control 110. The inkdischarge control unit 113 in the FPGA for control 110 selects aprinting type appropriate for the type of the recording medium Mindicated by the medium information. The printing type includes adischarging type of the ink discharged onto the recording medium M andresolution of the image formed on the recording medium M.

FIG. 25 is a diagram illustrating a relation between an optimum printingtype, and the types of the recording media and printing modes. FIG. 26is a diagram illustrating the discharging type and the resolutioncorresponding to each printing type. As illustrated in FIG. 26, aprinting type A is a type in which the recording head 6 discharges largedroplets of ink to form an image on the recording medium M with theresolution of 600 dpi. A printing type B is a type in which therecording head 6 discharges middle droplets of ink to form an image onthe recording medium M with the resolution of 600 dpi. A printing type Cis a type in which the recording head 6 discharges small droplets of inkto form an image on the recording medium M with the resolution of 600dpi. A printing type D is a type in which the recording head 6discharges middle droplets of ink to form an image on the recordingmedium M with the resolution of 1200 dpi. A printing type E is a type inwhich the recording head 6 discharges small droplets of ink to form animage on the recording medium M with the resolution of 1200 dpi.

As illustrated in FIG. 25, the ink discharge control unit 113 selectsany of the printing types A to E described above based on the type ofthe recording medium M indicated by the medium information from thecolorimetric camera 20 and a designated printing mode, and determinesthe discharging type of the ink to be discharged onto the recordingmedium M and the resolution of the image to be formed on the recordingmedium M. Four types of printing modes are prepared, that is, “fast(line drawing)”, “fast”, “standard”, and “high quality” in descendingorder of printing speed, and any of the printing modes is designated bythe user in advance. When the printing mode is not designated by theuser, as illustrated in FIG. 27, for example, a printing modepredetermined for each type of the recording medium M is automaticallyset. FIG. 27 is a diagram illustrating a relation between the type ofthe recording medium M and the printing mode that is automatically set.

For example, in a case in which the identified type of the recordingmedium M is any of the “plain paper”, the “recycled paper”, and the“inkjet plain paper”, the printing type A is selected when the printingmode is “fast (line drawing)”, and the printing type B is selected whenthe printing mode is other than “fast (line drawing)”. When theidentified type of the recording medium M is the “tracing paper”, theprinting mode of “fast (line drawing)” is not applied thereto, so thatthe printing type B is selected irrespective of the printing mode.

In a case in which the identified type of the recording medium M is the“mat film”, the printing type B is selected when the printing mode is“standard”, and the printing type C is selected when the printing modeis “high quality”. The printing modes of “fast (line drawing)” and“fast” are not applied to the “mat film”.

In a case in which the identified type of the recording medium M is the“mat coated paper”, the printing type A is selected when the printingmode is “fast (line drawing)”, the printing type C is selected when theprinting mode is “fast”, the printing type B is selected when theprinting mode is “standard”, and the printing type D is selected whenthe printing mode is “high quality”.

In a case in which the identified type of the recording medium M is the“coated paper”, the printing type C is selected when the printing modeis “fast”, the printing type B is selected when the printing mode is“standard”, and the printing type D is selected when the printing modeis “high quality”. The printing mode of “fast (line drawing)” is notapplied to the “coated paper”.

When the identified type of the recording medium M is the “glossypaper”, the printing mode that supports the “glossy paper” is only “highquality”, so that the printing type E is selected. In a case in whichthe identified type of the recording medium M is the “semi-glossypaper”, the printing type C is selected when the printing mode is“fast”, the printing type B is selected when the printing mode is“standard”, and the printing type E is selected when the printing modeis “high quality”. The printing mode of “fast (line drawing)” is notapplied to the “semi-glossy paper”.

According to the embodiment, the ink discharge control unit 113 in theFPGA for control 110 determines the discharging type and the resolutionaccording to the type of the recording medium M identified by theidentifying unit 47. Alternatively, the discharging type and theresolution may be determined by the CPU 101. In this case, the inkdischarge control unit 113 controls the operation of the recording head6 to perform image formation on the recording medium M with thedischarging type and the resolution determined by the CPU 101 inaccordance with a command from the CPU 101.

When the identifying unit 47 cannot identify the type of the recordingmedium M, as described above, the medium information indicating that thetype of the recording medium M cannot be identified is transmitted fromthe colorimetric camera 20 to the notification unit 116 in the FPGA forcontrol 110. In this case, for example, the notification unit 116 causesthe operation panel 17 to display a predetermined message to notify theuser using the image forming apparatus 100 that the type of therecording medium M cannot be identified, that is, the recording medium Mused for image formation is a recording medium M unknown to the imageforming apparatus 100. Through this notifying operation of thenotification unit 116, the user can recognize that the recording mediumM is unknown to the image forming apparatus 100. In this case, forexample, when information for identifying the type of the unknownrecording medium M is registered, identification by the identifying unit47 is enabled from this point forward.

FIG. 28 is a flowchart illustrating an example of processing ofgenerating and storing the information for identifying the type of theunknown recording medium M, and specifically illustrates a processingprocedure for storing, in the nonvolatile memory 45, the range of 2σindicating the coordinate range in the RGB color space used for the“diffused reflection RGB data analysis”. The processing illustrated inthe flowchart of FIG. 28 is performed such that the user performs apredetermined input operation through the operation panel 17 to operatethe image forming apparatus 100 in a registration mode, for example.

First, the unknown recording medium M is set at a predetermined positionon the platen 16 (Step S301). The image of the recording medium M iscaptured by the two-dimensional image sensor 26 of the colorimetriccamera 20 mounted on the carriage 5 (Step S302), and the image data ofthe diffused reflection region is stored (Step S303). Next, it isdetermined whether a predetermined number (for example, thirty) ofpieces of image data of the diffused reflection region are stored (StepS304). If the number of pieces of stored image data is smaller than thepredetermined number (No at Step S304), an image capturing position onthe recording medium M is changed by moving the carriage 5 (Step S305),and the processing after Step S302 is repeated. If the number of piecesof stored image data reaches the predetermined number (Yes at StepS304), the RGB value is extracted from each of the predetermined numberof pieces of image data of the diffused reflection region, and the rangeof 2σ of distribution thereof is calculated (Step S306). The calculatedrange of 2σ is then stored in the nonvolatile memory 45 in associationwith the type of the recording medium M (Step S307).

The processing of storing, in the nonvolatile memory 45, the range of 2σindicating the coordinate range in the RGB color space used for the“diffused reflection RGB data analysis” has been described above. Tostore, in the nonvolatile memory 45, the range of 2σ indicating thecoordinate range in the L*a*b* color space used for the “diffusedreflection L*a*b* data analysis”, the range of 2σ may be calculated andstored in the nonvolatile memory 45 after converting the RGB value intothe L*a*b* value. As information related to the “specular reflectionhistogram data analysis”, the “diffused reflection histogram dataanalysis”, and the “specular reflection residual histogram dataanalysis”, a relation between the values of the recording medium M (thepeak value of the luminance histogram of the specular reflection region,the value of the standard deviation σ of the luminance histogram of thediffused reflection region, and the value of the standard deviation σ ofthe histogram of the residual) obtained through the above processing,and the first threshold Th1, the second threshold Th2, the thirdthreshold Th3, and the fourth threshold Th4 may be obtained and stored.

FIG. 29 is a flowchart illustrating an operation of the image formingapparatus 100 after the processing of identifying the type of therecording medium M is ended.

If the type of the recording medium M can be identified by theidentifying unit 47 (Yes at Step S401), the ink discharge control unit113 selects the printing type appropriate for the type of the recordingmedium M indicated by the medium information, and determines thedischarging type of the ink to be discharged onto the recording medium Mand the resolution of the image to be formed on the recording medium M(Step S402). According to the discharging type and the resolutiondetermined at Step S402, printing on the recording medium M is started(Step S403).

On the other hand, if the type of the recording medium M cannot beidentified (No at Step S401), for example, the notification unit 116causes the operation panel 17 to display a predetermined message tonotify the user that the type of the recording medium M cannot beidentified (Step S404), and determines whether to continue the printing(Step S405). The determination for continuing the printing can be made,for example, according to whether the user performs a certain operationfor instructing to continue the printing using the operation panel 17.

If the printing is continued (Yes at Step S405), various settings aboutthe recording medium M are made to be settings for the “plain paper”(Step S406), the ink discharge control unit 113 selects the printingtype appropriate for the “plain paper” at Step S402 and determines thedischarging type and the resolution, and the printing on the recordingmedium M is started according to the discharging type and the resolutionappropriate for the “plain paper” at Step S403. On the other hand, ifthe printing is not continued (No at Step S405), the processing is endedas it is.

As described in detail above with specific examples, according to theembodiment, the image of the recording medium M is captured by thetwo-dimensional image sensor 26, and the glossiness evaluation valueindicating the glossiness of the recording medium M, the surfaceroughness evaluation value indicating the surface roughness of therecording medium M, and the coloring evaluation value indicating thecoloring of the recording medium M are obtained using the image data ofthe specular reflection region and the image data of the diffusedreflection region in the image of the recording medium M. The type ofthe recording medium M is then identified by combining the determinationusing the glossiness evaluation value, the determination using thesurface roughness evaluation value, and the determination using thecoloring evaluation value. Accordingly, the type of the recording mediumM that could not be identified in the related art is enabled to beidentified, so that more various types of recording media M can beappropriately identified than in the related art.

According to the embodiment, determination can be performed with higheraccuracy to obtain an accurate evaluation value by acquiring the imagedata of the diffused reflection region from the image of the recordingmedium M captured under the illumination of the first light source 31that is arranged so that the specular reflection light from therecording medium M is not incident on the two-dimensional image sensor26, and acquiring the image data of the specular reflection region fromthe image of the recording medium M captured under the illumination ofthe second light source 32 that is arranged so that the specularreflection light from the recording medium M is incident on thetwo-dimensional image sensor 26.

According to the embodiment, optimum image formation can be performed onthe recording medium M to be used by determining, for example, thedischarging type of the ink to be discharged onto the recording medium Mand the resolution of the image to be formed on the recording medium Maccording to the identified type of the recording medium M.

According to the embodiment, the user can recognize that the recordingmedium M to be used for image formation is the recording medium Munknown to the image forming apparatus 100 by receiving a notificationindicating that the type of the recording medium M cannot be identified,and the user can determine whether to continue the printing, forexample.

When the type of the recording medium M cannot be identified,information used for identifying the type of the unknown recordingmedium M is generated to be stored in a storage unit such as thenonvolatile memory 45 in accordance with the operation by the user.Accordingly, this type of recording medium M can be appropriatelyidentified using the information from this point forward.

Modification of Colorimetric Camera

The following describes modifications (a first modification and a secondmodification) of the colorimetric camera 20 according to the embodiment.Hereinafter, the colorimetric camera 20 according to the firstmodification is referred to as a colorimetric camera 20A, and thecolorimetric camera 20 according to the second modification is referredto as a colorimetric camera 20B. In each modification, a componentcommon to that of the colorimetric camera 20 is denoted by the samereference sign, and redundant description will not be repeated.

First Modification

FIGS. 30A and 30B are vertical cross-sectional views of the colorimetriccamera 20A according to the first modification. The colorimetric camera20A according to the first modification includes common light sources 33in place of the first light source 31 and the second light source 32 inthe colorimetric camera 20 described above. Similarly to the first lightsource 31 described above, the common light sources 33 are positioned sothat the specular reflection light from the recording medium M outsidethe housing 23 and the specular reflection light from the referencechart 40 inside the housing 23 are not incident on the two-dimensionalimage sensor 26.

The colorimetric camera 20A according to the first modification includesoptical path changing mirrors 34 and 35 arranged therein for changing anoptical path of the common light source 33 close to the opening 25 inidentifying the medium to cause the specular reflection light from therecording medium M to be incident on the two-dimensional image sensor26. Each of the optical path changing mirrors 34 and 35 is configured tobe rotatable with a rotation axis as a fulcrum, and one surface thereofis a mirror face that reflects light. For example, the optical pathchanging mirror 34 is attached to the substrate 22 constituting theupper surface of the housing 23, and the optical path changing mirror 35is attached to a side wall of the frame body 21 close to the opening 25.A color of a surface of the optical path changing mirror 35 opposite tothe mirror face is, for example, black that absorbs light.

In the colorimetric camera 20A according to the first modification, thecommon light sources 33 are driven while the optical path changingmirrors 34 and 35 are in the state as illustrated in FIG. 30B, and theimage of the colorimetric pattern is captured by the two-dimensionalimage sensor 26 under the illumination of the common light sources 33.

In identifying the medium, first, the common light sources 33 are drivenwhile the optical path changing mirrors 34 and 35 are in the state asillustrated in FIG. 30B, and the image of the recording medium M iscaptured by the two-dimensional image sensor 26 under the illuminationof the common light sources 33. Then, the image data of the diffusedreflection region is acquired from the image of the recording medium M.Thereafter, each of the optical path changing mirrors 34 and 35 isrotated with the rotation axis as a fulcrum to be in the state asillustrated in FIG. 30A, and the common light sources 33 are driven. Inthis case, faces of the optical path changing mirrors 34 and 35 facingthe common light source 33 are mirror faces. Accordingly, light from thecommon light source 33 is sequentially reflected by the optical pathchanging mirrors 34 and 35 to be emitted onto the recording medium Moutside the housing 23. The specular reflection light that is regularlyreflected by the recording medium M is incident on the two-dimensionalimage sensor 26. In this state, the image of the recording medium M iscaptured by the two-dimensional image sensor 26. The image data of thespecular reflection region is then acquired from the image of therecording medium M.

The colorimetric camera 20A according to the first modification canidentify the type of the recording medium M using the image data of thespecular reflection region and the image data of the diffused reflectionregion that are acquired as described above through a method similar tothat of the colorimetric camera 20.

Second Modification

FIG. 31 is a vertical cross-sectional view of the colorimetric camera20B according to the second modification. The colorimetric camera 20Baccording to the second modification includes a dedicatedtwo-dimensional image sensor 36 used for acquiring the image data of thespecular reflection region in identifying the medium in addition to thetwo-dimensional image sensor 26. In the colorimetric camera 20Baccording to the second modification, the second light source 32 ispositioned so that the specular reflection light that is emitted fromthe second light source 32 and regularly reflected by the recordingmedium M outside the housing 23 is incident on the dedicatedtwo-dimensional image sensor 36.

In identifying the medium, first, the colorimetric camera 20B accordingto the second modification captures the image of the recording medium Mwith the two-dimensional image sensor 26 under the illumination of thefirst light source 31, and acquires the image data of the diffusedreflection region from the image of the recording medium M. Thereafter,the image of the recording medium M is captured by the dedicatedtwo-dimensional image sensor 36 under the illumination of the secondlight source 32, and the image data of the specular reflection region isacquired from the image of the recording medium M. Thus, the type of therecording medium M can be identified using the image data of thespecular reflection region and the image data of the diffused reflectionregion that are acquired as described above through a method similar tothat of the colorimetric camera 20 described above.

The colorimetric camera 20B according to the second modification isconfigured to cause the specular reflection light from the recordingmedium M to be incident on the dedicated two-dimensional image sensor36, so that the second light source 32 and the dedicated two-dimensionalimage sensor 36 can be relatively freely laid out.

Other Modifications

According to the embodiment described above, the colorimetric camera 20has a function of identifying the type of the recording medium M.Alternatively, the type of the recording medium M may be identifiedoutside the colorimetric camera 20 using the image of the recordingmedium M captured by the two-dimensional image sensor 26. For example,the CPU 101 or the FPGA for control 110 mounted on the main controlboard 120 of the image forming apparatus 100 can be configured toidentify the type of the recording medium M. In this case, thecolorimetric camera 20 is configured to transmit, to the CPU 101 or theFPGA for control 110, the image of the recording medium M captured bythe two-dimensional image sensor 26 or the image data of the specularreflection region and the image data of the diffused reflection regionextracted from the image in place of the medium information indicatingthe type of the recording medium M. That is, the colorimetric camera 20is constructed as an image capturing unit without the function ofidentifying the type of the recording medium M.

According to the embodiment described above, the image forming apparatus100 including the colorimetric camera 20 has the function of identifyingthe type of the recording medium M. However, the identification of thetype of the recording medium M is not necessarily performed inside theimage forming apparatus 100. For example, as illustrated in FIG. 32, animage forming system may be constructed in which the image formingapparatus 100 is connected to an external device 500 in a communicablemanner, the external device 500 may be made to have a function as theidentifying unit 47 for identifying the type of the recording medium M,and the colorimetric value may be calculated by the external device 500.That is, the image forming system is constructed to include an imagecapturing unit 200 (the configuration of which is the same as thecolorimetric camera 20 excluding the identifying unit 47) arranged inthe image forming apparatus 100, the identifying unit 47 arranged in theexternal device 500, and a communication module 600 that connects theimage capturing unit 200 with the identifying unit 47 (connects theimage forming apparatus 100 with the external device 500). As theexternal device 500, for example, a computer called a digital front end(DFE) can be used. As the communication module 600, communicationutilizing a network such as a LAN or the Internet can be used inaddition to wired or wireless P2P communication.

In a case of the above configuration, for example, the image formingapparatus 100 transmits, to the external device 500, the image of therecording medium M captured by the two-dimensional image sensor 26 ofthe image capturing unit 200, or the image data of the specularreflection region and the image data of the diffused reflection regionextracted from the image utilizing the communication module 600. Theexternal device 500 passes, to the identifying unit 47, the image of therecording medium M received from the image forming apparatus 100, or theimage data of the specular reflection region and the image data of thediffused reflection region, and identifies the type of the recordingmedium M through the method described above. The external device 500then transmits, to the image forming apparatus 100, the mediuminformation indicating the type of the recording medium M identified bythe identifying unit 47. The image forming apparatus 100 determines thedischarging type of the ink to be discharged from the recording head 6onto the recording medium M and the resolution of the image to be formedon the recording medium M based on the medium information received fromthe external device 500. Accordingly, the image forming apparatus 100can perform optimum image formation on the recording medium M to beused.

In the above embodiment, the image forming apparatus 100 is described asthe inkjet printer. Alternatively, the image forming apparatus 100 canbe applied to an electrophotography device. When the image formingapparatus 100 is applied to the electrophotography device, a conveyingspeed or a transferring condition of the recording medium M, atemperature of a fixing device, and/or the like may be changed dependingon the type of the recording medium M. Thereby, the image formingapparatus 100 can perform optimum image formation on the recordingmedium M to be used.

Control functions of the components constituting the image formingapparatus 100 and the colorimetric camera 20 according to the embodimentdescribed above can be implemented as hardware, software, or acombination thereof. To implement the control functions of thecomponents constituting the image forming apparatus 100 and thecolorimetric camera 20 according to the embodiment as software, aprocessor included in the image forming apparatus 100 or thecolorimetric camera 20 executes a computer program describing aprocessing sequence. The computer program executed by the processor is,for example, provided being incorporated in advance a ROM inside theimage forming apparatus 100 or the colorimetric camera 20, and the like.The computer program executed by the processor may be recorded andprovided in a computer-readable recording medium such as a compact discread only memory (CD-ROM), a flexible disk (FD), a compact discrecordable (CD-R), and a digital versatile disc (DVD), as an installableor executable file.

The computer program executed by the processor may be stored in acomputer connected to a network such as the Internet and provided bybeing downloaded via the network. Furthermore, the computer programexecuted by the processor may be provided or distributed via a networksuch as the Internet.

According to an embodiment, more variety of recording media than in therelated art can be appropriately identified.

Although the invention has been described with respect to specificembodiments for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art that fairly fall within the basic teaching herein setforth.

What is claimed is:
 1. A type identification device comprising: atwo-dimensional image sensor configured to capture an image of anobject; a reference chart being arranged at a position different fromthe object, and an image of the reference chart being captured by thetwo-dimensional image sensor; a first light source at such a positionthat diffused reflection light from the object and diffused reflectionlight from the reference chart are incident on the two-dimensional imagesensor; a second light source at such a position that specularreflection light from the object is incident on the two-dimensionalimage sensor; and an identification circuit configured to identify atype of the object based on the image of the reference chart and animage of the object captured by the two-dimensional image sensor underillumination of the first light source, and the image of the objectcaptured by the two-dimensional image sensor under illumination of thesecond light source.
 2. The type identification device according toclaim 1, wherein the reference chart is disposed on a predeterminedsurface of a housing, wherein the second light source is configured tocapture the image of the object through an opening of the housing,together with the reference chart, wherein the first light source isconfigured to illuminate the reference chart and the object from theinside of the housing, and wherein the second light source is configuredto illuminate the reference chart from the inside of the housing.
 3. Thetype identification device according to claim 2, wherein the first lightsource is disposed between the opening and the reference chart when thefirst light source, the opening and the reference chart are projected ona plane orthogonal to an optical axis of the two-dimensional imagesensor.
 4. The type identification device according to claim 1, whereinthe first light source includes two light sources, and wherein thetwo-dimensional image sensor is disposed between the two light sourceswhen the two-dimensional image sensor and the two light sources areprojected on a plane orthogonal to an optical axis of thetwo-dimensional image sensor.
 5. The type identification deviceaccording to claim 1, wherein the identification circuit is configuredto obtain a surface roughness evaluation value indicating surfaceroughness of the object from the image captured under illumination ofthe first light source to identify the type of the object using theobtained surface roughness evaluation value.
 6. The type identificationdevice according to claim 5, wherein the identification circuit isconfigured to obtain, as the surface roughness evaluation, a standarddeviation of a luminance histogram of a region in the image of theobject captured under illumination of the first light source.
 7. Thetype identification device according to claim 1, wherein theidentification circuit is configured to obtain a coloring evaluationvalue indicating coloring of the object from the image captured underillumination of the first light source to identify the type of theobject using the obtained coloring evaluation value.
 8. The typeidentification device according to claim 7, wherein the identificationcircuit is configured to obtain, as the coloring evaluation value, avalue representing a color of a pixel in the image of the objectcaptured under illumination of the first light source.
 9. The typeidentification device according to claim 8, wherein the identificationcircuit is configured to use a value representing a color in the imageof the reference chart captured under illumination of the first lightsource to obtain the value representing the color of the pixel in theimage of the object captured under illumination of the first lightsource.
 10. The type identification device according to claim 1, whereinthe identification circuit is configured to obtain a surface roughnessevaluation value indicating surface roughness of the object and acoloring evaluation value indicating coloring of the object from theimage captured under illumination of the first light source to identifythe type of the object using the obtained surface roughness evaluationvalue and the obtained coloring evaluation value.
 11. The typeidentification device according to claim 10, wherein the identificationcircuit is configured to obtain, as the surface roughness evaluationvalue, a peak value of a luminance histogram of a specular reflectionregion reflecting specular reflection light from the object in the imagecaptured under illumination of the second light source.
 12. The typeidentification device according to claim 10, wherein the identificationcircuit is configured to obtain, as the surface roughness evaluationvalue, a value of a standard deviation of a histogram of a residual thatis a difference between a luminance distribution in a specularreflection region reflecting specular reflection light from the objectin the image captured under illumination of the second light source, anda normal distribution.
 13. The type identification device according toclaim 1, wherein the identification circuit is configured to obtain aglossiness evaluation value indicating glossiness of the object from theimage captured under illumination of the second light source to identifythe type of the object using the obtained glossiness evaluation value.14. The type identification device according to claim 1, wherein theobject is a sheet.
 15. An ink discharge apparatus comprising: The typeidentification device according to claim 1; and a recording headconfigured to discharge ink to the object.
 16. The ink dischargeapparatus according to claim 15, wherein the two-dimensional imagesensor and the recording head are disposed on a carriage configured tomove over the object.